1. Field of the Invention
The present invention is generally directed toward paint booth air handling systems and, more particularly toward a method for conditioning exterior air for use in a paint booth.
2. Description of Related Art
In a spray booth for painting, for example, vehicle bodies that are continuously conveyed on a conveyor through the spray booth, the quality of the conditioned (booth ambient) air is very important. Typically, exterior (atmospheric) air is passed through a conditioning area prior to being sent into the spray booth. The conditioned air is directed by an intake fan to a plenum chamber and is discharged downwardly at a predetermined flow velocity into the spray booth. The conditioned air in the spray booth is drawn together with coating mists, including any evaporated organic solvents, and is discharged beneath the booth by an exhaust fan. This downward air flow can prevent the coating mist or dust, which would otherwise create quality defects on the vehicle paint surface, from scattering and drifting in the booth. The airflow also helps provide a safer working environment for operators in the spray booth.
To properly treat the exterior air, known spray booth systems pass exterior air through the conditioning area to adjust properties of the exterior air. The conditioning area includes filters to remove dust or contaminants, preheaters and reheaters to warm, humidifiers to humidify and cool, and cooling coils to cool the exterior air before sending the newly conditioned air at a certain temperature and humidity into the spray booth. This is a significant task since typical high production-volume vehicle spray booths require over 100,000 cubic feet per minute of airflow in order for painting to safely and properly occur.
To accomplish this, the known systems utilize a reactive control system in which outside weather data is collected by sensors at the inlet of the conditioning system in real time. Then, PLCs (programmable logic controllers) using PID (proportional-integral-derivative) control algorithms, determine the proper settings for the conditioning system to adjust the exterior air to a desired set point.
The set point has a specific dry-bulb temperature and relative humidity. The dry-bulb temperature is the temperature of air measured by a thermometer exposed to the air and shielded from radiation and moisture. The relative humidity is the ratio of the amount of water vapor in the air and the maximum amount of water vapor the air can hold at the same temperature.
A set point of a specific dry-bulb temperature and relative humidity can be located on a psychrometric chart. The psychrometric chart is a graph of the physical properties of the air at a constant pressure. The psychrometric chart relates various properties of the air, such as dry-bulb temperature, wet-bulb temperature, dew point temperature, relative humidity, humidity ratio, specific enthalpy, and specific volume. At a specific elevation, all of the properties of the air can be determined by initially knowing only two of the properties. Preferably, the data that makes up the psychrometric chart is stored in a lookup table in the controller, thereby simplifying control of the conditioning system.
These known systems do not account for what would be the most economical or the most energy efficient method to adjust the exterior air to the set point. Further, the set point is traditionally fixed within a predetermined range and does not change within the range depending on the condition of the exterior air. Nor do the known systems condition the exterior air based upon predicted future conditions of the exterior air. Accordingly, considerable room still exists in the technology to provide such a system that can achieve the desired results using less energy and/or costing less money to operate.
Therefore, there exists a need in the art for a method to better condition the exterior air that is used in the spray booth.